Middle-lower crust and mantle rocks are generally widely exposed in metamorphic core complex or gneiss dome,which is an ideal place to study the exhumation process related to regional extension and rheology.The Laojun...Middle-lower crust and mantle rocks are generally widely exposed in metamorphic core complex or gneiss dome,which is an ideal place to study the exhumation process related to regional extension and rheology.The Laojunshan metamorphic complex in southeastern Yunnan is located in a special tectonic position surrounded by the Cathaysia,Yangtze and Indochina blocks.It is composed of different metamorphic-deformation rocks and granitic intrusions.There also are many economic deposits(e.g.,tin and tungsten)that are spatially and genetically associated with the formation and exhumation of the Laojunshan gneiss dome.Based on detailed analysis of macro-and microscopic structure,stress field distribution and deformation condition,the tectonic units of the Laojunshan metamorphic complex show obvious characteristics of doming,as well as of typical structural units of metamorphic core complex.It has strongly deformed metamorphic gneiss core(footwall),detachment fault system and sedimentary cover(hanging wall)with lightly metamorphism and deformation.The footwall of gneiss dome presents a strongly ductile deformation domain,accompanied by different ages of granitic intrusions.The distribution of developed foliation and lineation within granitic gneisses are arc-shaped and radial,respectively,with a nearly N-S trending from the footwall to the hanging wall.Mylonitization of deformed rocks gradually weakens and transits to orthogneiss as it moves away from the detachment fault toward the footwall.The low angle detachment fault between the footwall and the hanging wall shows an arc-like shape feature.Mylonite fabrics are preserved in the deformed rocks of the detachment fault,which are mainly composed of chloritized schist,fault breccia,cataclasite and fault gouge.A large number of normal faults are developed in detachment faults and hanging wall,and their stress fields radiate in an arc around the footwall.Zircon U-Pb ages of amphibolite and granitic gneiss from the footwall range from 445 to 420 Ma,indicating the timing of Caledonian magmatic emplacement and the main formation period of the Laojunshan gneiss dome.U-Pb ages of the zircon metamorphic rims are 241-230 Ma,representing the timing of high temperature metamorphism and shortened deformation of the Indosinian collision.In this period,the Laojunshan gneiss dome experienced the tectonic compression in association with high temperature metamorphism-deformation,which was superimposed by detachment and extensional exhumation in association with intense hydrothermal interaction and mineralization in the late stage.展开更多
The Yardoi gneiss dome is located to the easternmost of the North Himalayan Gneiss Dome (NHGD),southern Tibet. It consists of metapelite,garnet amphibolite,granite and leucogranite,and is a key subject to constrain th...The Yardoi gneiss dome is located to the easternmost of the North Himalayan Gneiss Dome (NHGD),southern Tibet. It consists of metapelite,garnet amphibolite,granite and leucogranite,and is a key subject to constrain the formation and tectonic evolution of NHGD. SHRIMP zircon U/Pb data on the leucogranite yield an age of 35.3±1.1 Ma,which is substantially older than that of the similar leu-cogranites to the west. Sr and Nd isotope systematics indicate that this leucogranite was derived from partial melting of the mixed garnet amphibolite and metapelite. Our data suggest that (1) during the early stage of Himalayan magmatism,amphibolite dehydration melting overwhelmed that of the metapelite; and (2) such a melting at middle-lower crust might be a major factor that initiated the movement along the Southern Tibetan Detachment System (STDS).展开更多
The Paiku composite leucogranitic pluton in the Malashan gneiss dome within the Tethyan Himalaya consists of tourmaline leucogranite,two-mica granite and garnet-bearing leucogranite.Zircon U-Pb dating yields that(1)to...The Paiku composite leucogranitic pluton in the Malashan gneiss dome within the Tethyan Himalaya consists of tourmaline leucogranite,two-mica granite and garnet-bearing leucogranite.Zircon U-Pb dating yields that(1)tourmaline leucogranite formed at28.2±0.5 Ma and its source rock experienced simultaneous metamorphism and anatexis at 33.6±0.6 Ma;(2)two-mica granite formed at 19.8±0.5 Ma;(3)both types of leucogranite contain inherited zircon grains with an age peak at^480 Ma.These leucogranites show distinct geochemistry in major and trace elements as well as in Sr-Nd-Hf isotope compositions.As compared to the two-mica granites,the tourmaline ones have higher initial Sr and zircon Hf isotope compositions,indicating that they were derived from different source rocks combined with different melting reactions.Combined with available literature data,it is suggested that anatexis at^35 Ma along the Himalayan orogenic belt might have triggered the initial movement of the Southern Tibetan Detachment System(STDS),and led to the tectonic transition from compressive shortening to extension.Such a tectonic transition could be a dominant factor that initiates large scale decompressional melting of fertile high-grade metapelites along the Himalayan orogenic belt.Crustal anatexis at^28 Ma and^20 Ma represent large-scale melting reactions associated with the movement of the STDS.展开更多
Determination of the timing and geochemical nature of early metamorphic and anatectic events in the Himalayan orogen may provide key insights into the physical and chemical behavior of lower crustal materials during t...Determination of the timing and geochemical nature of early metamorphic and anatectic events in the Himalayan orogen may provide key insights into the physical and chemical behavior of lower crustal materials during the early stage of tectonic evolution in large-scale collisional belts.The Yardoi gneiss dome is the easternmost dome of the North Himalayan Gneiss Domes(NHGD),and contains three types of amphibolites with distinct mineral assemblage,elemental and radiogenic isotope geochemistry,as well as various types of gneisses.SHRIMP zircon U/Pb analyses on the garnet amphibolite and garnet-bearing biotite granitic gneiss yield ages of nearly peak metamorphism at 45.0±1.0 Ma and 47.6±1.8 Ma,respectively,which are 2 to 4 Ma older than the age for partial melting in migmatitic garnet amphibolite(43.5±1.3 Ma).Available data have demonstrated that ultra-high pressure metamorphism in the Tethyan Himalaya occurred at ～55 Ma,and high amphibolite facies to granulite facies metamorphism at 45 to 47 Ma.In addition,partial melting at thickened crustal conditions occurred at 43.5±1.3 Ma,which led to the formation of high Sr/Y ratios two-mica granites.The high-grade metamorphic rocks in the NHGD may represent the subducted front of the Indian continental lithosphere.In large collisional belts,fertile components in crustal materials could melt and form granitic melts with relatively high Na/K and Sr/Y ratios under thickened crustal conditions,significantly different from those formed by decompressional melting during rapid exhumation.展开更多
基金This work was financially supported by the National Key Research and Development Program(Grant No.SQ2017YFSF040030)the National Natural Science Foundations of China(Grant Nos.41972220&41722207).
文摘Middle-lower crust and mantle rocks are generally widely exposed in metamorphic core complex or gneiss dome,which is an ideal place to study the exhumation process related to regional extension and rheology.The Laojunshan metamorphic complex in southeastern Yunnan is located in a special tectonic position surrounded by the Cathaysia,Yangtze and Indochina blocks.It is composed of different metamorphic-deformation rocks and granitic intrusions.There also are many economic deposits(e.g.,tin and tungsten)that are spatially and genetically associated with the formation and exhumation of the Laojunshan gneiss dome.Based on detailed analysis of macro-and microscopic structure,stress field distribution and deformation condition,the tectonic units of the Laojunshan metamorphic complex show obvious characteristics of doming,as well as of typical structural units of metamorphic core complex.It has strongly deformed metamorphic gneiss core(footwall),detachment fault system and sedimentary cover(hanging wall)with lightly metamorphism and deformation.The footwall of gneiss dome presents a strongly ductile deformation domain,accompanied by different ages of granitic intrusions.The distribution of developed foliation and lineation within granitic gneisses are arc-shaped and radial,respectively,with a nearly N-S trending from the footwall to the hanging wall.Mylonitization of deformed rocks gradually weakens and transits to orthogneiss as it moves away from the detachment fault toward the footwall.The low angle detachment fault between the footwall and the hanging wall shows an arc-like shape feature.Mylonite fabrics are preserved in the deformed rocks of the detachment fault,which are mainly composed of chloritized schist,fault breccia,cataclasite and fault gouge.A large number of normal faults are developed in detachment faults and hanging wall,and their stress fields radiate in an arc around the footwall.Zircon U-Pb ages of amphibolite and granitic gneiss from the footwall range from 445 to 420 Ma,indicating the timing of Caledonian magmatic emplacement and the main formation period of the Laojunshan gneiss dome.U-Pb ages of the zircon metamorphic rims are 241-230 Ma,representing the timing of high temperature metamorphism and shortened deformation of the Indosinian collision.In this period,the Laojunshan gneiss dome experienced the tectonic compression in association with high temperature metamorphism-deformation,which was superimposed by detachment and extensional exhumation in association with intense hydrothermal interaction and mineralization in the late stage.
基金Supported by National Natural Science Foundation of China (Grant No.40673027)the Outlay Research Fund of Chinese Academy of Geological Sciences (Grant No.20071120101125)the Hundred Talent Program of Chinese Academy of Sciences
文摘The Yardoi gneiss dome is located to the easternmost of the North Himalayan Gneiss Dome (NHGD),southern Tibet. It consists of metapelite,garnet amphibolite,granite and leucogranite,and is a key subject to constrain the formation and tectonic evolution of NHGD. SHRIMP zircon U/Pb data on the leucogranite yield an age of 35.3±1.1 Ma,which is substantially older than that of the similar leu-cogranites to the west. Sr and Nd isotope systematics indicate that this leucogranite was derived from partial melting of the mixed garnet amphibolite and metapelite. Our data suggest that (1) during the early stage of Himalayan magmatism,amphibolite dehydration melting overwhelmed that of the metapelite; and (2) such a melting at middle-lower crust might be a major factor that initiated the movement along the Southern Tibetan Detachment System (STDS).
基金supported by the National Basic Research Program of China(2011CB403102)the National Natural Science Foundation of China(41073024 and 41273034)
文摘The Paiku composite leucogranitic pluton in the Malashan gneiss dome within the Tethyan Himalaya consists of tourmaline leucogranite,two-mica granite and garnet-bearing leucogranite.Zircon U-Pb dating yields that(1)tourmaline leucogranite formed at28.2±0.5 Ma and its source rock experienced simultaneous metamorphism and anatexis at 33.6±0.6 Ma;(2)two-mica granite formed at 19.8±0.5 Ma;(3)both types of leucogranite contain inherited zircon grains with an age peak at^480 Ma.These leucogranites show distinct geochemistry in major and trace elements as well as in Sr-Nd-Hf isotope compositions.As compared to the two-mica granites,the tourmaline ones have higher initial Sr and zircon Hf isotope compositions,indicating that they were derived from different source rocks combined with different melting reactions.Combined with available literature data,it is suggested that anatexis at^35 Ma along the Himalayan orogenic belt might have triggered the initial movement of the Southern Tibetan Detachment System(STDS),and led to the tectonic transition from compressive shortening to extension.Such a tectonic transition could be a dominant factor that initiates large scale decompressional melting of fertile high-grade metapelites along the Himalayan orogenic belt.Crustal anatexis at^28 Ma and^20 Ma represent large-scale melting reactions associated with the movement of the STDS.
基金supported by the National Natural Science Foundation of China (41073024 and 40921001)the National Basic Research Program of China (2011CB403102)the Outlay Research Fund of Institute of Geology (J1004)
文摘Determination of the timing and geochemical nature of early metamorphic and anatectic events in the Himalayan orogen may provide key insights into the physical and chemical behavior of lower crustal materials during the early stage of tectonic evolution in large-scale collisional belts.The Yardoi gneiss dome is the easternmost dome of the North Himalayan Gneiss Domes(NHGD),and contains three types of amphibolites with distinct mineral assemblage,elemental and radiogenic isotope geochemistry,as well as various types of gneisses.SHRIMP zircon U/Pb analyses on the garnet amphibolite and garnet-bearing biotite granitic gneiss yield ages of nearly peak metamorphism at 45.0±1.0 Ma and 47.6±1.8 Ma,respectively,which are 2 to 4 Ma older than the age for partial melting in migmatitic garnet amphibolite(43.5±1.3 Ma).Available data have demonstrated that ultra-high pressure metamorphism in the Tethyan Himalaya occurred at ～55 Ma,and high amphibolite facies to granulite facies metamorphism at 45 to 47 Ma.In addition,partial melting at thickened crustal conditions occurred at 43.5±1.3 Ma,which led to the formation of high Sr/Y ratios two-mica granites.The high-grade metamorphic rocks in the NHGD may represent the subducted front of the Indian continental lithosphere.In large collisional belts,fertile components in crustal materials could melt and form granitic melts with relatively high Na/K and Sr/Y ratios under thickened crustal conditions,significantly different from those formed by decompressional melting during rapid exhumation.
